Thermo- and chemical-triggered overhand and reef knots based on liquid crystal gels

Abstract

A knot is a worldwide used complication and one of the most ancient technologies in human history. A knot can be found in a wide range of applications such as providing practical structural robustness and mechanical connections between objectives. Here, we report a responsive knot that can self-adjust its geometry upon external stimuli. The knot is tightened in a thread made of a liquid crystal gel, the diameter and internal friction of which vary upon thermal/chemical stimulus. An overhand knot and a reef knot are demonstrated to exhibit auto-untie action responsive to external stimuli. A self-dropping device is shown to sense its surrounding temperature and chemical change in the environment, providing the proof-of-concept for sensing application. The results offer new alternatives for soft micro-robots and automation control for non-electric devices.